Webs or batts containing absorbent fibers have been used for a number of years in products such as diapers, sanitary napkins and the like. These webs are conventionally made of cellulose fibers and provide a relatively inexpensive absorbent matrix. Webs of cellulosic fibers however do have some disadvantages. As these webs become wet, they contract and the capillaries which provide the basis for absorption tend to collapse. As a result of this contraction, the web becomes stiff and the potential absorbent capacity present is not utilized. Attempts have been made recently to provide a batt or web of mixed fibers, i.e., one containing thermoplastic fibers. These fibers, while not absorbent in themselves, remain resilient when exposed to aqueous based fluids. Also, they have the effect of spacing the individual cellulosic fibers and, as a result, tend to inhibit the collapse of individual capillaries due to the wetting of the web. An example of such a web is disclosed in U.S. Pat. No. 4,100,324 issued to Anderson and Sokolowski.
Recently there have been a class of absorbent compounds introduced which, while not as inexpensive as cellulose can, under ideal conditions, absorb a substantially greater amount of fluid than cellulose. These materials which are available in both powder and fibrous form, have much smaller capillaries than cellulose as a rule. This class of material is particularly susceptible to early failure as an absorbent when the absorbing fluid is viscous and/or contains suspended particles. When these improved absorbents are used for the uptake of menses or blood, they fail to absorb at a capacity anywhere near their capacity for less viscous fluids. (These materials, e.g. phosphorylated pulp, carboxymethylcellulose, modified rayon, etc. are those generally referred to throughout the specification as those which are more highly absorbent with an equal volume of cellulose fibers under ideal conditions of an aqueous based essentially nonviscous fluid.)
The problem of premature failure as an absorbent of these increased absorbency compounds has been recognized and the primary thrust of attempts to minimize this premature failure has been to increase the surface area of these materials relative to the remainder of the web in which they are placed. One of the most promising approaches has been the combination of individual particulate superabsorbents with meltblown microfiber. (The process for manufacture of a web containing meltblown microfibers is disclosed in U.S. Pat. No. 3,676,242.) This latter approach is described in British Application No. 8233488, has met with some success with regard to transporting and immobilizing fluid along the planar surface formed by the meltblown microfibrous web.
While this latter process more effectively utilizes superabsorbent material, in a situation where more absorbency is needed than can be provided on the surface of an absorbent web, the small capillaries of the meltblown microfiber coupled with the small capillaries of the extra absorbent material distributed throughout its planar surface, inhibit the downward, i.e., z direction transfer of fluid. This situation is particularly exacerbated when the fluid is viscous such as menses or blood.